When a protection apparatus (for example, an active hood) on a vehicle front part is activated in thecase where a collision object is not a pedestrian (human being), various undesirable influences arise. For example, when discrimination from a pedestrian cannot be made in the case where a collision occurs with a light object such as a construction signboard, the protection apparatus is unnecessarily activated and a repair cost incurs.
Besides, when discrimination from a pedestrian cannot be made in the case where a collision occurs with a heavy fixture such as a concrete wall or a vehicle, the hood moves back in a state where it is raised. In this instance, the hood enters a vehicle interior and damages a passenger in the vehicle. Thus, it is conventionally requested to accurately discriminate whether or not a collision object is a pedestrian.
JP-A-11-028994 proposes to discriminate a pedestrian by using a time period (duration of continuation) when a collision load (or deformed amount) exceeds a predetermined level. U.S. Pat. No. 6,561,301 (JP-A-11-310095) proposes to discriminate a pedestrian by using an increasing rate after a collision load exceeds a predetermined level.
Another prior art proposes to discriminate a pedestrian based on a peak value of a collision load. That is, in these prior arts, a pedestrian is discriminated from another collision object based on predetermined change components of the collision load detection signal waveform.
However, the collision objects have various shapes and various rigidities. Even if they have the same speed and the same mass, waveforms of the collision load F(=m×a) vary according to these shapes and stiffness. Thus, the accurate pedestrian discrimination is difficult when only the above duration time of the collision load, the increasing rate or the peak value is used.
For example, in the case where the collision object is a wide body in the vehicle width direction (lateral direction), the deformation of a vehicle body such as a bumper in the width direction is large. As a result, the collision load per unit area (for example, unit width) acting on the collision object or the vehicle body becomes small, and the deformation in the depth direction (longitudinal direction) of the collision object or the vehicle body becomes small.
On the contrary, in the case where the width of the collision object is narrow, the collision width of the vehicle body is small (narrow). As a result, the collision load per unit area (for example, unit width) acting on the collision object or the vehicle body becomes large, and the deformation of the collision object or the vehicle body in the depth direction become large. The collision load detection signal waveform changes with the degree of the depressed deformation of the collision object or the bumper.